In the prior art, the belt applies a great pressure to the shoulders of a user. To improve this defect, a shoulder protection portion is formed on the belt so as to reduce the pressure on the shoulders. The protection portion is formed by fiber cloth or sponges. However the elastic coefficients of the fiber cloth and sponge are small. The protection portion will fatigue elastically or deform after being used for a longer time period or as the bag supported by the belt is heavy. Thereby the prior art is a not a preferred one, which can not improve the prior art defect completely.